Florida children in grades six through eight are required under current law to take one semester of physical education every year, but the state is now considering a bill to eliminate the requirement for that class.

The bill's sponsor, Republican State Rep. Larry Metz, said in an email to ABC News that one of the main reasons behind the proposed law is to leave the decision to offer physical education up to local school districts, not the state. He is not opposed to physical education, he said, and the bill would not affect the current physical education requirement in elementary schools.

"Simply because an idea may have merit for some does not mean that we should use the power of government to mandate it for all," Metz wrote. "Some physically fit and active middle school students might rather use that time in their school day to take another elective."

He added that it was difficult for some schools to accommodate the additional time required for physical education while trying to focus on academic achievement. It would have required lengthening the school day, in some cases, and there was no "additional funding" to do that.

"Since this mandate was passed, K-12 education funding has been significantly reduced," Metz said. "In the current declining revenue environment, I believe it is only fair that some mandates on school districts be removed."

But nutritionists, pediatricians and the American Heart Association are all speaking out against the bill, saying that with obesity affecting 30 percent of the nation's children, cutting back on physical education is dangerous.

"If we don't get our middle school children being physically active as early as possible, we run the risk of more obesity and more bad habits developing as we age," said Dr. Ralph Sacco, immediate past president of the American Heart Association and professor of neurology at the University of Miami's Miller School of Medicine.

Physical education programs have been cut in schools across the country. But in some states, schools have brought the programs back, said Keith Ayoob, associate professor of pediatrics at the Albert Einstein College of Medicine in the Bronx, N.Y.

"Physical education is healthy, and kids who are more physically fit are better able to focus on academics," Ayoob said. "There's also good evidence that in school districts where there are regular recess periods, there are fewer diagnoses of ADHD [attention-deficit hyperactivity disorder]."

The lead author of a new study published online in Obesity Journal said her research shows that targeting obesity through exercise and diet at an early age is even more essential than originally believed.

Sarah Messiah, a research associate professor of pediatrics at the University of Miami's Miller School of Medicine, and her colleagues found that obese children as young as 3 are showing risk factors for heart disease such as elevated levels of fat in the blood and elevated levels of a protein linked to heart disease and organ damage.

While it's still not known how old these children, if they remain overweight or obese, will be when disease develops, Messiah said the study suggests it could be a lot earlier than people think. Many believe that obesity predisposes a child to develop serious disease as an adult, but it could be that disease hits sometime during childhood if risk factors are present in preschoolers.

"I think the whole paradigm has downshifted in terms of when these risk factors can translate into overt disease, both cardiovascular disease and diabetes," Messiah said.

With research showing that even very young obese children may be at risk for developing heart disease, strokes and diabetes, Messiah said, it's especially important to encourage physical activity.

"In light of this new evidence, children could potentially be at the start of the cardiovascular risk process, and about one-third of our nation's children are overweight or obese," Messiah said. "One of the only lines of defense is physical activity, and taking it away doesn't make much sense."